..... auto-ignition temperature and flame front propagation speed.

When the spark ignites the mixture, a flame front spreads into the combustion chamber, sending ahead of itself a pressure shock that heats the unburned mixture as it passes through it. If the shock wave is strong enough to raise the air/fuel mixture to its auto-ignition temperature, the whole charge detonates at once, even before the flame front reaches the detonation point. However the strength of the flame front generated shock wave depends very much on the flame front propagation speed, and that is not only a function of the auto-ignition temperature because, by definition, the flame front exceeds the auto-ignition temperature. Actually the combustion reaction rate must be slowed as well. That's the job of additives.

Nowadays, primarily aromatics appear to be added to raise the octane rating of pump gas. They seem to be both denser and of equivalent heat of combustion as gasoline. That could explain the higher heat content of 93 vs. 87 octane pump gas.

VonK


"Not dead yet...!" (Monty Python)

"A little bit of knowledge is a dangerous thing." (unknown)


vonk at bayarea dot net


All statements, quotations and illustrations by VonK are to be construed as his
opinions only, and not as advice, consent, recommendation, guidance, instruction,
and/or suggestion.